The invention relates generally to charge reversible polymers, peptides and their resulting colloidal particles and, more specifically, to easily hydrolysable amides that are relatively stable at neutral pH but quickly hydrolyze at low pH.
Cationization is a potent approach to enhance cellular uptake by electrostatically adsorptive endocytosis of macromolecules and colloidal particles such as proteins, nanoparticles and liposomes. For instance, cationic photosensitizer chlorine-6 (ce6)-conjugate with cationic polylysine had up to 17 times higher cellular uptake of ce6. This enhanced endocytosis is of great importance in cancer-targeted drug delivery because intracellular drug release from liposomes, polymer-drug conjugates, and polymeric micelles or nanoparticles can circumvent membrane-associated multidrug resistance. Cationic polymers such as polyethyleneimine (PEI) can also disrupt lysosomal membranes, which is useful for drug delivery to cytosol. Nuclear localization signals (NLS), which are short highly positively charged basic peptides that actively transport large molecules across the nuclear membrane and localize cargo molecules (to which they have been conjugated) from the cytosol to the cell nucleus, is also useful for nuclear drug/gene delivery.
The in vivo applications of those positively charged macromolecules or colloidal particles, however, is very limited because cationic charges can cause severe serum inhibition and rapid clearance from the plasma compartment, and sequestered to mainly in the liver. For instance, a cationized antibody had a 58-fold increase in the systemic clearance from the plasma compartment and a 9-fold reduction in the mean residence time as compared to the native antibody. Such a fast plasma clearance makes them impossible to reach their targeted tissues other than the liver or intracellular compartment.
Most cancer chemotherapy drugs, such as anthracyclines and cisplatin, target nuclear DNA to cause DNA damage and/or topoisomerase inhibition to induce cell death (apoptosis). In addition to the overexpressed multidrug-resistance mechanism in the cell membrane, drug-resistant cancer cells have many intracellular drug-resistance mechanisms to limit the access of cytosolic drugs to the nucleus. Consequently, only a small percentage of drugs delivered into the cytosol finally reach the nucleus. For example, less than 1% of the cisplatin molecules that enter the cell actually bind the nuclear DNA. Thus, a drug carrier capable of localizing and directly releasing drugs into the nucleus would circumvent the multidrug-resistance and intracellular drug-resistance mechanisms to effectively deliver drugs to the vicinity of DNA, leading to a high therapeutic efficacy.
Polymer nanoparticles can carry drugs preferentially to cancerous tissues by means of the enhanced permeation and retention (EPR) effect and bypass the multidrug resistance in the cell membrane, but the nanoparticles developed to date were found retained in cytoplasmic organelles including lysosomes rather than the nucleus. Nuclear localization peptides (NLPs)—short highly positively charged peptides that actively transport large proteins across the nuclear membrane—have been used to localize drug molecules from the cytosol to the nucleusA cationic polymer, polyethyleneimine (PEI), has been used extensively in nonviral gene delivery. It can carry DNA across the cell membrane, harness the molecular motors to actively move along the microtubule network, and finally enter the nucleus. NLPs and PEI, however, are highly positively charged at physiological pH. Positively charged polymers or colloidal particles can cause severe serum inhibition and are rapidly cleared from the plasma compartment, and thus cannot be used in vivo.
An ideal regime would be to activate the cationic charges only in cancerous tissues or their intracellular compartments. In the present invention, nanoparticles with a negative-to-positive charge-reversal PEI outer layer triggered by the solid tumor extracellular acidity (pH<7) or lysosomal (pH 4-5) for nuclear drug delivery. Negatively charged polymers have little interaction with the blood components and have been used extensively in vivo.